The virtue of Lailat Al-Qadr and the Exhortation to seek it; When it is and the most likely times to seek it Sahih Muslim 1165 f
Arabic hadith text
وَحَدَّثَنَا مُحَمَّدُ بْنُ الْمُثَنَّى، حَدَّثَنَا مُحَمَّدُ بْنُ جَعْفَرٍ، حَدَّثَنَا شُعْبَةُ، عَنْ جَبَلَةَ، قَالَ سَمِعْتُ ابْنَ عُمَرَ، - رضى الله عنهما - يُحَدِّثُ عَنِ النَّبِيِّ صلى الله عليه وسلم أَنَّهُ قَالَ "مَنْ كَانَ مُلْتَمِسَهَا فَلْيَلْتَمِسْهَا فِي الْعَشْرِ الأَوَاخِرِ "
Translation
Ibn Umar (Allah be pleased with them) reported Allah's Messenger (ﷺ) as saying
He who is anxious to seek it (Lailat-ul-Qadr) should seek it in the last ten (nights of Ramadan).